Mammalian DNA polymerases alpha, beta, gamma, delta, and epsilon incorporate fialuridine (FIAU) monophosphate into DNA and are inhibited competitively by FIAU Triphosphate.
ABSTRACT Fialuridine [FIAU, 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5- iodouridine] was used in clinical trials for chronic hepatitis B virus infection and was extremely toxic. Evidence suggested targets of FIAU toxicity included mitochondria, but toxic mechanisms were unclear. Since FIAU is a thymidine analog, we reasoned that triphosphorylated FIAU (FIAUTP) could be incorporated into mitochondrial DNA by DNA pol-gamma and into genomic DNA by DNA polymerases alpha, beta, delta, and epsilon. All five purified mammalian DNA polymerases incorporated FIAUMP into the nascent DNA chain during in vitro DNA synthesis. When FIAUTP was substituted for dTTP, oligonucleotide products were generated efficiently by DNA pol-gamma and were similar to those generated in the presence of the four normal dNTPs. In contrast, oligonucleotide products generated by the four nuclear DNA polymerases in the presence of FIAUTP were significantly reduced in length relative to those generated in the presence of dTTP. In parallel kinetic assays, FIAUTP competitively inhibited the accumulation of radiolabeled dTTP into DNA by DNA pol-gamma. The Ki with DNA pol-gamma was 0.04 microM, the lowest Ki among the mammalian DNA polymerases. Competition between FIAUTP and dTTP and the relative ease of accumulation of FIAUMP in mitochondrial DNA by DNA pol-gamma in vitro together may relate to clinical FIAU toxicity.
SourceAvailable from: Hubert G M Niesters[Show abstract] [Hide abstract]
ABSTRACT: Background: Lamivudine is a non-toxic, potent inhibitor of hepatitis B virus replication. Recently, hepatitis B virus resistance to lamivudine has been described in patients using immunosuppressive drugs after liver transplantation.Methods: From our cohort of 81 consecutive patients treated with lamivudine, we selected all immunocompetent patients who received lamivudine monotherapy for a period over 26 weeks (n=14).Results: Lamivudine resistance with the characteristic mutation in the YMDD motif was observed in four patients (actuarial cumulative incidence: 39%). Two patterns of viral resistance were observed; incomplete response (n=2) and viral breakthrough (n=2).Conclusions: The observed high frequency of lamivudine resistance may have implications for the concept of long-term virus-suppressive therapy of chronic hepatitis B by lamivudine monotherapy.Journal of Hepatology 07/1997; 26(6):1393-1395. DOI:10.1016/S0168-8278(97)80476-X · 10.40 Impact Factor
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ABSTRACT: We examined the effects of sugar-modified nucleotide analogs on the reaction with DNA polymerase γ and HIV reverse transcriptase. The 3′-modified derivative, 3′-amino-3′-deoxythymidine 5′-triphosphate inhibited the reaction of both enzymes. However, where it did not cause chain termination in the DNA polymerase y reaction, it did cause termination in HIV reverse transcriptase reaction. On the other hand, the triphosphate derivative of oxetanocin G which has a 3, 4-dihydroxymethyloxetane at the sugar moiety instead of ribofuranose showed the chain termination in both polymerase reactions, however, termination sites with DNA polymerase γ reaction were different from those with HIV reverse transcriptase or with DNA polymerase α. These results, combined with our previous data, indicate that the action of several sugar-modified nucleotide analogs on DNA polymerase γ could be very different from those on other eukaryotic DNA polymerases including HIV reverse transcriptase.1. This paper is dedicated to Dr. Yoshihisa Mizuno on the occasion of his 75th birthday.Nucleosides Nucleotides & Nucleic Acids 01/1996; 15(1-3):683-692. DOI:10.1080/07328319608002415 · 0.89 Impact Factor
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ABSTRACT: The intersection of aging and HIV/AIDS is a looming 'epidemic within an epidemic.' This paper reviews how HIV/AIDS and its therapy cause premature aging or contribute mechanistically to HIV-associated non-AIDS illnesses (HANA). Survival with HIV/AIDS has markedly improved by therapy combinations containing nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors, and protease inhibitors (PIs) called HAART (highly active antiretroviral therapy). Because NRTIs and PIs together prevent or attenuate HIV-1 replication, and prolong life, the population of aging patients with HIV/AIDS increases accordingly. However, illnesses frequently associated with aging in the absence of HIV/AIDS appear to occur prematurely in HIV/AIDS patients. Theories that help to explain biological aging include oxidative stress (where mitochondrial oxidative injury exceeds antioxidant defense), chromosome telomere shortening with associated cellular senescence, and accumulation of lamin A precursors (a nuclear envelop protein). Each of these has the potential to be enhanced or caused by HIV/AIDS, antiretroviral therapy, or both. Antiretroviral therapy has been shown to enhance events seen in biological aging. Specifically, antiretroviral NRTIs cause mitochondrial dysfunction, oxidative stress, and mitochondrial DNA defects that resemble features of both HANA and aging. More recent clinical evidence points to telomere shortening caused by NRTI triphosphate-induced inhibition of telomerase, suggesting telomerase reverse transcriptase (TERT) inhibition as being a pathogenetic contributor to premature aging in HIV/AIDS. PIs may also have a role in premature aging in HIV/AIDS as they cause prelamin A accumulation. Overall, toxic side effects of HAART may both resemble and promote events of aging and are worthy of mechanistic studies.Laboratory Investigation advance online publication, 16 December 2013; doi:10.1038/labinvest.2013.142.Laboratory Investigation 12/2013; DOI:10.1038/labinvest.2013.142 · 3.83 Impact Factor